1. Field of the Invention
The present invention relates to a scroll compressor, and more particularly, to a vacuum preventing device for a scroll compressor in which gas in a discharge region flows backward to a suction region at the time of an abnormal driving such as a pump down or an expansion valve blocking, thereby preventing a vacuum of the compressor.
2. Description of the Background Art
Generally, a compressor is a device for converting mechanical energy into latent energy of a compression fluid, and is largely classified into a reciprocation compressor, a scroll compressor, a centrifugal compressor, and a vane compressor by compression methods.
The scroll compressor has a structure that gas is sucked, compressed, and discharged by using a rotation member like the centrifugal type and the vane type differently from the reciprocating type which uses a linear reciprocation of an piston member.
FIG. 1 is a longitudinal sectional view showing an inner part of the conventional scroll compressor.
As shown, the scroll compressor comprises: a case 1 divided into a gas suction pipe SP and a gas discharge pipe DP; a main frame 2 and a sub frame (not shown) respectively installed at both sides of upper and lower portions of an inner circumference surface of the case 1; a driving motor 3 installed between the main frame 2 and the sub frame; a rotation shaft 4 engaged to a center portion of the driving motor 3 for transmitting a rotation force of the driving motor 3; an orbiting scroll 5 installed to have an eccentric rotation at an upper portion of the rotation shaft 4 and having a wrap 5a of an involute curve shape at the upper portion thereof; and a fixed scroll 6 engaged to the orbiting scroll 5, and having a wrap 6a of an involute curve shape so as to form a plurality of compression spaces P therein.
The case 1 is divided into a suction region S1 and a discharge region S2 by a high and low pressure separation plate 7, and a compression region S3 is formed at a position connected to the compression space P.
A gas inlet 6b and an outlet 6c are respectively formed at a lateral surface and a center portion of the fixed scroll 6, and a non-return valve 8 for preventing discharged gas from flowing backward is installed at an upper surface of the fixed scroll 6.
The main frame 2 and the sub frame are fixed to the inner circumference surface of the case 1 by a fixation means such as welding, and the fixed scroll 6 is also fixed to a bottom surface of the high and low pressure separation plate 7 by a fixation means such as a bolt.
Meantime, in case of a pump down and an expansion valve blocking, the suction region S1 of the compressor becomes a high vacuum state. At this time, components relevant to the compressor may be damaged and destroyed.
To prevent this, a vacuum preventing device 20 is provided in the conventional art.
FIG. 2 is a longitudinal sectional view showing an operation at the time of a normal driving in the vacuum preventing device of FIG. 1, FIG. 3 is a longitudinal sectional view showing an operation at the time of an abnormal driving in the vacuum preventing device of FIG. 1, and FIG. 4 is a sectional view taken along line A—A of FIG. 2.
Referring to FIGS. 2 and 3, the vacuum preventing device 20 includes a chamber 10 formed at one side of the fixed scroll 6, and a discharge hole 11 connected to the discharge region S2 at an upper surface of the chamber 10.
A compression hole 12 connected to the compression region S3 is formed at a bottom surface of the chamber 10, a plug 14 having a suction hole 13 is fixed to an opening portion of the chamber 10 by a fixation pin 15, and the suction hole 13 is connected to the discharge hole 11.
An open/close member 17 for selectively connecting the discharge hole 11 and the suction hole 13 is movably installed in the chamber 10.
A spring 16 for limiting a movement of the open/close member 17 and providing an elasticity force thereto is installed at the opening portion of the chamber 10.
Hereinafter, operations of the conventional scroll compressor will be explained.
First, when a power source is applied to the driving motor 3, the driving motor 3 rotates the rotation shaft 4, and the orbiting scroll 5 engaged to the rotation shaft 4 is rotated to an extent of its eccentric distance.
At this time, a plurality of compression spaces P formed between the wrap 5a of the orbiting scroll 5 and the wrap 6a of the fixed scroll 6 gradually move towards a center portion of the fixed scroll 6 as the orbiting scroll 5 continuously performs an orbiting movement, thereby having a decreased volume.
By the decreased volume of the compression spaces P, gas of the suction region S1 is sucked into the compression space P through the inlet 6b, and the sucked gas is discharged to the discharge region S2 through the outlet 6c. 
When the compressor is normally driven, a pressure of the compression region is larger than an elasticity force of the spring 16, so that the open/close member 17 overcomes the elasticity force of the spring 16 and closes the discharge hole 11.
However, the compressor is abnormally driven, a pressure of the compression region is smaller than the elasticity force of the spring 16, so that the open/close member 17 is shoved by the elasticity force of the spring 16 and opens the discharge hole 11. At this time, the discharge hole 11 is connected to the suction hole 13.
As the discharge hole 11 and the suction hole 13 are connected to each other, gas of the discharge region S2 flows backward into the suction region S1 through the discharge hole 11 and the suction hole 13, thereby releasing a vacuum of the compressor.
As shown in FIG. 4, in the conventional scroll compressor, a minute clearance t is formed between an inner wall of the chamber 10 and an outer circumference surface of the open/close member 17 so as to induce a smooth slide movement of the open/close member 17.
Generally, the clearance is fabricated as the minimum size so that the open/close member 17 can slide the chamber 10, and fabricated as a minute size enough not to leak gas through the discharge hole 11 when the open/close member 17 closes the discharge hole 11.
When the clearance t becomes smaller, gas is closed more efficiently but an operation of the open/close member 17 is not smooth. On the contrary, when the clearance t becomes larger, gas leakage is increased and an operation of the open/close member 17 is smooth. Accordingly, considering the operation of the open/close member 17, the clearance t is designed and fabricated within a tolerance limit range.
However, in the conventional art, when the compressor is normally driven, the open/close member 17 receives a pressure downwardly by a gas pressure of the discharge region S2. At this time, a bottom surface of the open/close member 17 is adhered to an inner bottom surface of the chamber 10 and an upper surface of the open/close member 17 is more separated from an inner upper surface of the chamber 10. That is, the clearance t becomes large more than the tolerance limit range.
When the clearance t becomes large, a part of gas of the discharge region leaks to the suction region through the clearance, thereby degrading a compression efficiency of the compressor.
Also, in the conventional art, since high minuteness is required at the time of designing and fabricating the clearance, a high cost is required and a productivity is degraded.